The present invention relates to data recording and, more particularly, to a method and apparatus for discriminating acceleration events and recording only those that meet pre-determined criteria.
A wide variety of recording devices have been developed to sense and record numerous physical variables such as shock, vibration, strain, force, temperature, humidity, and even barometric pressure. Because of their ability to measure and record such a broad range of variables, these devices have many applications. For example, data recorders are commonly used in the transportation industry to detect and record the environmental conditions experienced by cargo during transportation and handling. The data collected by the recorders is later analyzed and used to determine how the transportation and handling process can be improved or to determine where, during the transportation process, the cargo was damaged.
In another application, data recorders are used to detect and record seismic activity. These devices may be used, for example, in the construction and mining industries to detect and record the energy of vibrations generated by explosive charges.
Data recording devices typically record data in either a continuous format or a discrete format. Continuous recording devices simply record data continuously from the start to the end of a recording session. This technique is not well suited to collecting data over long recording sessions because large amounts of memory are needed to store the data. In addition, large amounts of labor are involved in the data reduction and processing.
Discrete recording devices record only portions of the data detected during the recording session. Because they do not record data continuously, they are better suited for use in applications requiring longer recording sessions. A discrete recording device records segments of data at either 1) periodic intervals (time-based recording) or 2) upon the occurrence of a "trigger" event (event-based recording). For example, a time-based recorder may record a short segment of data every three minutes, while an event-based recorder may record a segment of data each time one of the sensed variables satisfies a pre-determined criterion.
Time-based recorders provide an adequate overview of a recording session. However, such recorders may not adequately record an impact or other occurrence. If an impact or other acceleration event occurs during a non-recording interval, vital data concerning the moment of impact will be lost. The recorder may detect and record only the aftermath of such an occurrence during its recording interval.
Even event-based recorders sometimes do not provide sufficient information about an acceleration event for proper analysis. Typically, recorders record either the entire acceleration history or only peak acceleration levels. Recording the entire acceleration history requires large amounts of data storage and labor for analysis. Recording only the peak acceleration levels often provides insufficient information to properly analyze the damage potential of the acceleration event.